Ferroelectric capacitor and method for fabricating the same

Abstract

In a ferroelectric capacitor comprising: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, the coercive voltage of the ferroelectric film is 1.5 V or less and the polarization switching time of the ferroelectric film is 200 ns or less.

Description

BACKGROUND OF THE INVENTION[0001](a) Fields of the Inventions[0002]The present invention relates to ferroelectric memory devices using dielectric materials, and to ferroelectric capacitors and their fabrication methods capable of enhancing the speed at which the polarization of a ferroelectric film is reversed.[0003](b) Description of Related Art[0004]In the development of ferroelectric memory devices, in order to fabricate the devices having stack structures with a large capacity of 256 kbit to 4 Mbit, a significant increase in degree of integration of the devices, that is, miniaturization of the devices is indispensable. Moreover, the devices are required to operate at high speed.[0005]For example, a first conventional example (see, for example, Japanese Laid-open Patent Publication No. H7-99252) proposes the high-speed operation method as described below. In the case where a ferroelectric film made of PZT(PbZrxTi1−xO3) with a ferroelectric crystal structure of ABO3 (where A and B...

AI Technical Summary

Benefits of technology

[0010]To attain the above object, a ferroelectric capacitor according to a first aspect of the present invention comprises: a lower electrode; a ferroelectric film formed on the lower electrode; and an upper electrode formed on the ferroelectric film, and when the coercive voltage of the ferroelectric film is 1.5 V or less, the polarization switching time of the ferroelectric film is 200 ns or less. With this ferroelectric capacitor, excellent polarization switching characteristics and stable operation can be provided. The ferroelectric film employed in this capacitor has a layered perovskite structure composed of SrBi2(Ta1−xNbx)2O9 (commonly known as SBTN), and the thickness of the ferroelectric film is 120 nm or less.

[0011]In the ferroelectric capacitor according to the first aspect of the present invention, when the coercive voltage of the ferroelectric film is 1.0 V or less, the polarization switching time of the ferroelectric film is 100 ns or less. With this ferroelectric capacitor, more excellent polarization switching characteristics and stable operation can be provided. The ferroelectric film employed in this capacitor has a layered perovskite structure composed of SrBi2(Ta1−xNbx)2O9, and the thickness of the ferroelectric film is 80 nm or less.

[0012]In the ferroelectric capacitor according to the first aspect of the present invention, when the coercive voltage of the ferroelectric film is 0.6 V or less, the polarization switching time of the ferroelectric film is 20 ns or less. With this ferroelectric capacitor, much more excellent polarization switching characteristics and stable operation can be provided. The ferroelectric film employed in this capacitor has a layered perovskite structure composed of SrBi2(Ta1−xNbx)2O9, and the thickness of the ferroelectric film is 50 nm or less.

[0015]As shown above, the present invention can offer the ferroelectric capacitor which prevents degradation of ferroelectric materials during a semiconductor fabrication process, particularly a decrease in electric properties due to approaches for ferroelectric thickness reduction and low-voltage operation associated with miniaturization of semiconductors, and which conducts excellent high-speed operation and stable operation.

Problems solved by technology

In the first conventional example, since the Curie temperature Tc of the ferroelectric is lowered, the capacitor operates unstably at high temperatures.

This in turn degrades the characteristics of retention or imprint reliabilities thereof.

Moreover, the process stability is also unstable, and it is still difficult to fully prevent degradation in the stability.

As a result of this, degradation in polarization switching characteristics is remarkable.

Images